In the use of relatively insensitive, low cost industrial explosives based on ammonium nitrate-fuel combinations it is usually necessary to use primers or booster charges containing some sort of high explosive in order to obtain efficient detonation. Otherwise a substantial portion of the ammonium nitrate is often undecomposed after the explosion. In the past both dynamite and primers of cast solid high explosive have been used. The high explosive materials are conventionally melted and poured into containers of the type exemplified by U.S. Pat. Nos. 3,183,836 and 3,604,353. The containers, or canisters for the cast high explosive primers are usually fitted with a lid or cap which is pressed on after the molten explosive has cooled and solidified.
There have recently become available cap-sensitive aqueous gel ammonium nitrate explosives which would be desirable for use in primers. U.S. Pat. No. 3,962,001 discloses an explosive of this type. Unfortunately the explosive primer canisters which are already in use are unsuitable for aqueous gel explosive. Having been designed for melt-casting high explosive compositions, they are difficult to fill with an aqueous gel or do not have enough structure to hold a gel while retaining their physical shape. In general they are also too small for the purpose. The fabrication of a cylindrical canister with an open central longitudinal passage and adjacent well for a detonator presents difficulties, particularly when it is necessary to make the container longer than conventional primers, and make it contain a shapeless gel. Prior art designs for waterproof or leak-proof primer canisters, as in U.S. Pat. No. 3,354,827 have been difficult to seal and have required too much hand assembly at the blasting site.